expected array behaviour

[Mike James]

I have a function that uses 2 array strings defined similar to this...

const char[] array1 = ABCDEFGHIJKLMNOPQRSTUVWXYZ;
char[]  array2 = ABCDEFGHIJKLMNOPQRSTUVWXYZ;

If I make a change to a char in array1 it also changes the same in array2.
But if I define the arrays as follows...

const char[26] array1 = ABCDEFGHIJKLMNOPQRSTUVWXYZ;
char[26]  array2 = ABCDEFGHIJKLMNOPQRSTUVWXYZ;

It doesn't occur. Is this expected behaviour?

Regards,
-=mike=-

Re: expected array behaviour

[John Reimer]

Hello Mike,


I have a function that uses 2 array strings defined similar to this...

const char[] array1 = ABCDEFGHIJKLMNOPQRSTUVWXYZ; char[]  array2 =
ABCDEFGHIJKLMNOPQRSTUVWXYZ;

If I make a change to a char in array1 it also changes the same in
array2. But if I define the arrays as follows...

const char[26] array1 = ABCDEFGHIJKLMNOPQRSTUVWXYZ; char[26]  array2
= ABCDEFGHIJKLMNOPQRSTUVWXYZ;

It doesn't occur. Is this expected behaviour?

Regards,
-=mike=-



Wha?!  If that's true, that looks like a nasty bug!

Is that dmd v2 or v1? Linux or Windows?

-JJR

Re: expected array behaviour

[Mike James]

Forgot to mention - Windows XP.

Regards,

-=mike=-

Re: expected array behaviour

[Jarrett Billingsley]

On Thu, Jan 1, 2009 at 6:56 PM, Mike James f...@bar.com wrote:
 Hi John,

 I am using D1.038, dsss and Tango.

 I've written a quick example but this one is even stranger...

 

 module main;

 import tango.io.Stdout;

 int main() {
func1();
func2();

return 0;
 }

 void func1() {
char[] array1 = ABCD;
char[] array2 = ABCD;

Stdout(array1).newline;
Stdout(array2).newline;
Stdout.newline;

array2[0] = 'Z';

Stdout(array1).newline;
Stdout(array2).newline;
Stdout.newline;
 }

 void func2() {
char[4] array1 = ABCD;
char[4] array2 = ABCD;

Stdout(array1).newline;
Stdout(array2).newline;
Stdout.newline;

array2[1] = 'Q';

Stdout(array1).newline;
Stdout(array2).newline;
Stdout.newline;
 }

 

 Regards,

 -=mike=-


If you want to modify the contents of string literals, like you're
doing here, put a .dup on them.

char[] array1 = ABCD.dup;

Again, modifying the contents of string literals is illegal and the
results are undefined.

Re: expected array behaviour

[Jarrett Billingsley]

On Thu, Jan 1, 2009 at 7:10 PM, Mike James f...@bar.com wrote:
 Got it - so I should do this...

 const char[] array1= ABCDEFGHIJKLMNOPQRSTUVWXYZ;
 char[]  array2 = new char[array1.length];

Just char[] array2 = array1.dup;

.dup duplicates the array by creating a new array the same length and
copying the data over.

Re: expected array behaviour

[John Reimer]

Hello Jarrett,


If you want to modify the contents of string literals, like you're
doing here, put a .dup on them.

char[] array1 = ABCD.dup;

Again, modifying the contents of string literals is illegal and the
results are undefined.




Oh, right.  I missed that.

-JJR

Re: expected array behaviour

[John Reimer]

Hello Jarrett,


On Thu, Jan 1, 2009 at 5:55 PM, Mike James f...@bar.com wrote:


I have a function that uses 2 array strings defined similar to
this...

const char[] array1 = ABCDEFGHIJKLMNOPQRSTUVWXYZ; char[]  array2 =
ABCDEFGHIJKLMNOPQRSTUVWXYZ;

If I make a change to a char in array1 it also changes the same in
array2. But if I define the arrays as follows...


You'd get a runtime error if you were using Linux.  For some reason
string literals are not read-only, or Windows doesn't respect it, or
something like that.  Modifying either array1 or array2 is technically
illegal.  So, uh, don't do it.




Yes, that's one advantage to Linux.  String literals aren't read-only on 
Win32.  This is unfortunate because it means that these sort of bugs are 
significantly harder to diagnose on Windows than on Linux.  I remember that 
this was a bug in a early DUI version (now GtkD).  It's was pretty easy to 
spot on Linux because of the runtime error.


-JJR